An issue was discovered in PHP through 7.2.2. The php-fpm master process restarts a child process in an endless loop when using program execution functions (e.g., passthru, exec, shell_exec, or system) with a non-blocking STDIN stream. This allows a remote attacker to generate a DoS on Shared Hosting Services, performed by this php-fpm master process consuming 100% of the CPU and disk space with a large volume of error logs.
https://bugs.php.net/bug.php?id=70185 [php 5.4]
https://bugs.php.net/bug.php?id=75968 [php 7.2]
Created php tracking bugs for this issue:
Affects: fedora-all [bug 1547726]
The Red Hat Product Security Team does not consider this issue as a security flaw because specially crafted PHP scripts (containing embedded operating system commands) are required to trigger this flaw.
Correction to "containing embedded operating system commands": no embedded operating system commands are needed, only 2 php scripts are needed to CPU-DOS a shared hosting server without leaving a trace where the high load comes from, making it impossible to detect which hosting customer is to blame for.
copy from PHP Bug #75968: